The invention relates to a method of detecting a welding process voltage, between a welding torch an a workpiece, comprising the step of performing a calculation of the welding process voltage in real time, taking account of the interference variables, in particular an inductance and a resistance of a welding system.
Document DE 197 17 462 A1 discloses a method and a switching system for detecting interference variables and determining arc voltage, in which an actual value for the working voltage is reduced to the sum of the partial voltage releases relevant to the actual welding process needed to control the welding current source via the arc and via the end of the electrode through which the welding current flows, so that only the effective resistance values are used for control purposes, without additionally having to involve in the control system any interference variables which influence the control system and hence the transmissibility, comparability, reproducibility, process stability and finally welding quality. In this method, the detected working voltage is transmitted to a welding current source, the working voltage being detected externally to the output terminals of the current source as a sum of the partial voltage releases relevant to the actual welding process via an arc and via an end of an electrode through which the welding current flows, as well as via a resistance of the workpiece, additional measuring lines being provided for the detection process. These are connected to a controller so that the drop in voltage can be measured or detected via these measuring lines.
The disadvantage of this arrangement is that providing additional lines considerably increases the amount of wiring needed for a welding process and the parallel transmission to the welding lines gives rise to extra interference signals which affect the measuring lines and have to be compensated at great technical expense and which can lead to faulty measurements.
The underlying objective of the invention is to propose a method of detecting the welding process voltage, whereby the calculated or detected interference variables of the welding process voltage can be incorporated in the control process without incurring significant expense.
This objective is achieved by the invention by performing the calculation for determining inductance at a specific time interval during a welding process without the welding process being affected. This makes it possible to adapt to the control speed or to the requisite welding quality so that welding processes can be run at a very high control rate and to a high welding quality. The advantage of this arrangement is also that the interference variables can be detected without the need for additional hardware, thereby avoiding any external influences. Another advantage resides in the fact that the calculation method used to determine the interference variables can be run continuously or periodically, which means that in the case of a pulse welding process, a control can be applied during the entire duration of the pulse, making it possible to use or generate very short pulses without having to extract a corresponding range that is not controllable, as is necessary with the prior art.
It is also of advantage to apply the calculated welding process voltage by a control unit to the welding process. This produces a very high welding quality because the interference variables can be taken into account in the process control.
It is additionally of advantage if the interference variable are detected and/or calculated by the control unit before the start of the actual welding process because this obviates the need for an additional control device for the detection or calculation process and instead this calculation can be operated by the control device used to regulate the process.
A standardised structure can be used for the equipment if a voltage and a current at the outputs of the current source are measured by a measuring device.
The welding process control is optimised and older welding equipment or welding current sources can be simply and inexpensively improved by means of a software update if a welding process control is performed during the entire pulse duration and the interference variables are calculated by the control unit by means of software using the detected values and a predetermined calculation program.
The invention will be described with reference to an example of an embodiment.